Femoral stem offset adjustment system

Abstract

The present invention relates to a femoral stem offset adjustment system (1) for adjusting a femoral implant (2) relative to the intramedullary canal (3) of the femur, the adjustment system (1) comprising a femoral support (5), a user-adjustable element (6), a stem support (7), a first link member (8) that rotatably holds the user-adjustable element (6) at the femoral support (5), a second link member (9) that rotatably couples the user-adjustable element (6) and the stem support (7) together, and a third link member that slidably connects the user-adjustable element (6) and the stem support (7), wherein at least two of the first link member (8), the second link member (9), and the third link member, preferably their longitudinal axes, are arranged substantially in a common plane, the plane being perpendicular to the axis of rotation.

Description

Technical Field

[0001] The present invention relates to arthroplasty, particularly knee arthroplasty and total knee arthroplasty. More specifically, the present invention relates to a device that enables a surgeon to efficiently and accurately align a femoral implant with the intramedullary canal of the femur. In particular, the present invention relates to a femoral stem offset adjustment system / device / instrument (hereinafter also referred to as an adjustment system or adjustment instrument).

Background Art

[0002] The knee joint enables the human leg to bend or articulate during movement. At the knee, the lower bone (tibia) contacts the upper bone (femur). Proximally at the knee, the femur has two protrusions known as femoral condyles. The femoral condyles engage with fibrocartilage at the upper end of the tibia. The knee joint is held by ligaments, capsules, muscles, and tendons. In the knee structure, four ligaments are particularly prominent, with one ligament on each side of the knee and two ligaments in the center. Of the central ligaments, one ligament faces forward and the other faces backward. The patella or kneecap is a bone fragment supported in front of the knee joint. Functionally, the patella serves as a shield.

[0003] The knee joint can become nearly or completely non-functional due to long-term overuse, disease, or trauma. The best treatment is often total replacement (arthroplasty). In total knee arthroplasty, the surfaces of the femur and tibia that articulate at the knee are completely replaced. The first step in this process is to remove the articular surface and the underlying portion. The distal end of the femur is resected to provide clearance for the femoral implant component. Similarly, the proximal portion of the tibia is resected to provide a flat surface for the tibial implant component. A person's body weight transfers from the head of the femur near the hip joint to the ankle. Appropriate knee alignment must be maintained when installing the femoral artificial device (implant) and the tibial artificial device (implant) to enable continued appropriate weight transfer. For the prosthetic to function properly, not only the femoral and tibial surfaces resulting from these resections but also the femoral implant and the tibial implant must be accurately aligned. Additionally, the femoral and tibial implants must be appropriately spaced to stabilize knee flexion and extension.

[0004] Once the bone is appropriately prepared to receive the artificial component, the surgeon typically utilizes a "trial" system of artificial components provided by the manufacturer of the prosthetic. Trial components are sample artificial components available in various sizes and shapes and are intended to be temporarily placed on the prepared bone to evaluate the exact size, shape, and precise alignment, adjustment, and orientation in the actual patient. A femoral stem offset adjustment system is used to adjust the offset position of the (trial) femoral component relative to the intramedullary canal of the femur.

[0005] Furthermore, to evaluate the flexion and extension gaps between the femoral implant and the tibial implant, the patient undergoes a trial reduction using blocks / templates of various thicknesses. This trial reduction means moving the joint including the trial implant with typical motions selected for that joint. If the knee is unstable or not properly aligned, for example, a thicker or thinner tibial implant may be used.

[0006] In known femoral stem offset adjustment systems, the offset adjustment is to be performed at a certain location, but due to the structure and size of the adjustment system, the adjustment system protrudes beyond the (trial) femoral implant. In particular, to adjust the offset in any direction, usually a rotational movement and a sliding movement guided in one direction are combined, so the system requires a certain installation space, especially in the axial direction, due to the various relative movabilities of the connecting parts. Particularly disadvantageous is that in order to correctly evaluate the flexion and extension gaps, the adjustment system has to be removed, which is time-consuming and results in an additional working step.

[0007] Therefore, there may be a need for a better femoral stem offset adjustment system with a compact and small structure that can perform offset adjustment and sizing of the extension and flexion gaps while the adjustment system remains attached to the patient so that the surgeon can quickly and efficiently align the (trial) femoral implant. SUMMARY OF THE INVENTION

[0008] This object is solved by a femoral stem offset adjustment system having the features of claim 1. Further advantageous developments of the invention are made for the subject matter of each of the dependent claims.

[0009] The femur stem offset adjustment system is for adjusting (properly positioning) a (trial) femoral implant (instrument), particularly a lower limb femoral implant, with respect to (relative to) the intramedullary canal of the femur. The femur stem offset adjustment system is particularly for adjusting the offset position of the femoral implant with respect to a (trial) stem corresponding to the intramedullary canal.

[0010] The adjustment system comprises a femur support portion. The femur support portion is adapted to be (fixedly / statically / non-rotatably and non-displaceably) connected to the femoral implant. For example, the femur support portion may be fixedly attached to the femoral implant by femur attachment elements such as screws or pins.

[0011] Furthermore, the adjustment system comprises a user adjustment element. The user adjustment element may be formed by a knob-like element such as a wheel. The user adjustment element is preferably formed as a manually operable adjustment wheel (grasped by a surgeon). The user adjustment element is held / received by the femur support portion so as to be rotatable about a rotation axis. That is, the user adjustment element is attached to the femur support portion such that the femur support portion and the user adjustment element are rotatably held relative to each other (the user adjustment element is connected to the femur support portion so as to rotate about a rotation axis relative to the femur support portion). The rotation axis preferably corresponds to the longitudinal axis of the adjustment system / the axis of the intramedullary canal. Thus, the offset direction (clock position) of the femur support portion (i.e., the femoral implant) with respect to the user adjustment element can be set.

[0012] Furthermore, the adjustment system comprises a stem support. The stem support is adapted to be (fixedly / statically / non-rotationally and non-displaceably) connected to the intramedullary canal. In particular, the stem support is adapted to be connected to a stem corresponding to the intramedullary canal of the femur. The stem support is integrally rotatably connected to a user adjustment element. That is, the stem support is attached to the user adjustment element such that the stem support and the user adjustment element are rotationally connected to each other (the stem support is connected to the user adjustment element so as to rotate integrally with the user adjustment element). Furthermore, the stem support is slidably received / connected to the user adjustment element along a sliding axis. Preferably, the stem support is slidably received in the user adjustment element in one direction. That is, the stem support is connected to the user adjustment element so as to be slidable along the sliding axis with respect to the user adjustment element. The sliding axis is perpendicular to the rotational axis (i.e., perpendicular to the longitudinal axis of the adjustment system). Thus, the offset amount of the stem support (i.e., the stem) with respect to the user adjustment element can be set. Since the femur support rotates freely with respect to the user adjustment element, the sliding axis along which the user adjustment element and the stem support are slidable relative to each other rotates with the relative rotation between the user adjustment element and the femur support, and as a result, the combination of the relative rotation and the one-direction relative sliding is converted to adjust the offset position between the femur support and the stem support in any direction.

[0013] In other words, the femoral stem offset adjustment system functionally connects the femoral implant to the stem so that the offset direction and offset amount can be adjusted to adjust the offset position. The offset direction is set by rotating the femoral support portion (together with the stem support portion) about the axis of rotation with respect to the user adjustment element. The offset amount is set by sliding the user adjustment element (together with the femoral support portion) with respect to the stem support portion along a sliding axis perpendicular to the axis of rotation. Accordingly, the femoral stem offset adjustment system provides a sliding adjustment along the sliding axis, and the sliding axis is rotatable about the axis of rotation. Accordingly, the femoral implant can be displaced relative to the stem in any direction perpendicular to the axis of rotation.

[0014] According to the present invention, the femoral stem offset adjustment system includes, at the femoral support portion, a first link member / portion that rotatably holds the user adjustment element, a second link member / portion that rotatably connects the user adjustment element and the stem support portion, and a third link configuration (member / portion) that slidably connects the user adjustment element and the stem support portion. The rotatable holding by the first link member, the integrally rotatable connection by the second link member, and the slidable connection by the third link configuration coexist. Further, the rotatable holding by the first link member, the integrally rotatable connection by the second link member, and the slidable connection by the third link configuration are preferably brought about by a form fit and are defined by the structure / geometric shape of the first link member, the second link member, and the third link member / configuration.

[0015] At least two of the first link member, the second link member, and the third link configuration / member, preferably their longitudinal axes, are arranged on a substantially common plane. It is preferable that the first link member and the second link member are arranged on a substantially common plane. The common plane is perpendicular to the axis of rotation. Substantially on a common plane means not only the exact arrangement on the plane and the tolerance range of the plane, but also an arrangement within a common axial range that can extend from 0 mm (exact arrangement on the plane) to a maximum of 10 mm along the axis of rotation (a slight axial offset between at least two of the first link member, the second link member, and the third link member), preferably up to a maximum of 5 mm (a small axial offset between at least two of the first link member, the second link member, and the third link member).

[0016] In other words, two or all of the first link member, the second link member, and the third link member (longitudinal axes) are arranged on a (common) plane. By arranging the link members on the same plane, the femoral stem offset adjustment system becomes shorter in the direction perpendicular to the plane, i.e., the length along the axis of rotation / longitudinal direction, and has an axially compact design. When the size of the femoral stem offset adjustment system is small, the adjustment system can be integrated into the (trial) femoral implant, especially the thickness of the (trial) femoral implant, so that the adjustment system does not protrude beyond the femoral implant. Therefore, the trial reduction of the extension gap and the flexion gap can be performed while the adjustment system is arranged. This has the advantage that the surgeon can perform the adjustment saving time.

[0017] In short, according to the present invention, at least two of the first link member, the second link member, and the third link member (providing a functional connection between the femoral support portion, the user adjustment element, and the stem support portion), preferably at least the first link member and the second link member, are not axially spaced apart as proposed by the prior art, but are radially spaced apart / nested / aligned. By being grouped on essentially the same radial plane (i.e., within the same axial range), an axially short adjustment device can be provided.

[0018] According to a preferred embodiment, the first link member and the second link member may be integrally formed by a fastening element. In other words, the first link member and the second link member may be formed by the same component. That is, the fastening element can not only allow the user adjustment element to rotate freely relative to the femoral support portion, but also connect the user adjustment element to rotate integrally with the stem support portion. The integrated design of the two functions (of the first and second link members) requires reducing the number of components. Further, since the first and second link members are formed by the same component, their longitudinal axes coincide, that is, they are necessarily arranged on the same plane. This means that, as described above, the axial design of the adjustment system becomes smaller.

[0019] According to a preferred embodiment, the radially outer portion of the fastening element may form the first link member, and the radially inner portion of the fastening element may form the second link member. In this way, in order to reduce the axial length of the adjustment system, the link members may be arranged side by side in the radial direction. In other words, the fastening element is arranged radially between the femoral support portion and the user adjustment element (connecting them to be rotatable freely relative to each other), and is arranged radially between the user adjustment element and the stem support portion (connecting them to be non-rotatable relative to each other).

[0020] According to a preferred embodiment, the fastening element may be formed by two pins. These pins may be coaxially arranged with respect to each other. These pins may be axially spaced apart. Preferably, these pins may be arranged at (circumferentially) opposite positions of the stem support, in particular so as to contact the stem support. The circumferentially opposite arrangement is advantageous because it prevents (in addition to preventing relative rotation) the radial (i.e., the direction perpendicular to the circumferential direction) translation of the stem support with respect to the pins (i.e., with respect to the user adjustment element).

[0021] According to a preferred embodiment, the first link member may engage with the circumferential groove of the femoral support. Preferably, the circumferential groove may be formed on the inner circumferential surface of the femoral support. In order to provide 360° free rotation / rotation of the user adjustment element with respect to the femoral support, the circumferential groove may be a 360° circumferential groove. Preferably, the first link member may engage with the circumferential groove such that the user adjustment element and the femoral support are translationally connected to each other.

[0022] According to a preferred embodiment, the second link member may engage / contact the outer edge surface of the stem support. The outer edge surface may be perpendicular to the longitudinal axis of the second link member. Accordingly, translation of the stem support with respect to the user adjustment element in the direction along the outer edge surface, i.e., in the direction perpendicular to the longitudinal axis of the second link member, is possible. In other words, the second link member engages with the outer edge surface of the stem support such that sliding movement is possible. The second link member may preferably engage axially beyond the axial end face of the stem support. Accordingly, only translation in a direction perpendicular to the axial / rotation axis and perpendicular to the radial direction is possible. Accordingly, the engagement between the outer edge surface and the second link member (fastening element) guides the movement in one direction along the sliding axis. A single component, i.e., the fastening element, not only enables all the necessary relative movements but also fixes the components (user adjustment element, stem support, femoral support) to each other (stops all other relative movements of the components).

[0023] According to a preferred embodiment, the third link configuration / member may be formed by a first sliding portion of the stem support portion and a sliding guide portion of a user adjustment element that receives the first sliding portion. The sliding guide portion and / or the first sliding portion may have a rectangular shape that is long in the direction of the sliding axis. Accordingly, the sliding movement may be guided by the shape fit of these parts. The first sliding portion is preferably disposed distally with respect to the outer edge surface. Further, the sliding guide portion is preferably disposed distally with respect to the fastening element.

[0024] According to a preferred embodiment, the third link configuration / member may be formed by a fastening element and a second sliding portion of the stem support portion, particularly the radially inner portion of the fastening element. In particular, the third link configuration may be formed by the axial end face of the fastening element and a second sliding portion of the stem support portion that receives the axial end face of the fastening element. The second sliding guide portion may have a rectangular shape that is long in the direction of the sliding axis. The second sliding guide portion may form an outer edge surface, whereby the radially inner portion of the fastening element is guided by contacting the outer edge surface, enabling a sliding movement along the sliding axis. Accordingly, the sliding movement may be guided by the shape fit of these parts. Also, the integral design of the second sliding guide portion and the outer edge surface can provide a compact configuration of the adjustment system.

[0025] According to a preferred embodiment, the femoral stem offset adjustment system may include an offset direction scale that indicates the adjusted rotational position of the user adjustment element with respect to the femoral support portion. For example, the offset direction scale may be formed by numbers on the outer peripheral surface of the user adjustment element, particularly spaced equidistantly. Further, the offset direction scale may be formed by reference marks on the femoral support portion, particularly on the circumferential surface of the femoral support portion. Accordingly, the final implant can be easily positioned in the same offset direction as the trial femoral implant.

[0026] According to a preferred embodiment, the femoral stem offset adjustment system may comprise an offset amount scale indicating the adjusted sliding position of the user adjustment element relative to the stem support. Thus, the final implant can be easily positioned with the same offset amount as the trial femoral implant.

[0027] According to a preferred embodiment, the offset amount scale may be formed by a window of the user adjustment element and an offset mark on the (axial) end face of the stem support. According to a preferred embodiment, the femoral stem offset adjustment system may further comprise a femoral implant connected to the femoral support. The axial end face of the user adjustment element may be proximal to the axial end face of the femoral implant. That is, the axial end face of the user adjustment is recessed axially / longitudinally with respect to the femoral implant. Thereby, the adjustment instrument can be left attached during the evaluation of the extension gap and the flexion gap.

[0028] In other words, the object of the present invention is to have a femoral stem offset adjustment system that enables the flexion gap and the extension gap to be performed with the instrument placed. The goal of the instrument is to position the femoral implant in the best position with reference to the intramedullary canal. The adjustment system enables this positioning thanks to a 360° free rotation adjustment system with an additional offset of 0 to 5 mm. The design of the adjustment system further enables the trial reduction of the flexion gap and the extension gap with the adjustment system in place. This is thanks to an instrument design that allows the instrument to be grouped to the thickness of the trial femur.

[0029] The adjustment system comprises a user adjustment element (wheel), which is a rotating part indicating the clock position of the instrument when properly positioned within the femoral intramedullary canal. Due to two pins of the wheel and a groove in the femoral support, this user adjustment element does not rotate in the femoral support. The adjustment system comprises a (trial) femoral support, which is a component enabling the fixation of the adjustment system to the trial femur. The adjustment system comprises a (trial) stem support, which is a component connectable to the (trial) stem. The (trial) stem support is rotationally (360° freely) connected to the wheel and, furthermore, due to the rectangular shape of both components, enables a translation of 0 - 5 mm (offset). The offset value is displayed in a window of the wheel. The inner part of the pin fixed to the wheel enables the joining of both components (trial stem support and wheel) while allowing translation. The outer part of the pin fixed to the wheel enables free rotation within the femoral support due to an inner groove in the femoral support. The rectangular shape of both components (trial stem support and wheel) enables a translation (offset) between the wheel and the trial stem support.

[0030] Thus, thanks to the minimal design of the adjustment system not exceeding the thickness of the trial femoral component, trial reduction of the flexion gap and the extension gap can be performed. The dimensions of the adjustment system enable the performance of both the flexion gap and the extension gap, with the main advantage that gap management can be performed without removing the adjustment system, thereby saving time and facilitating the workflow.

Brief Description of the Drawings

[0031] The present invention will be described in more detail hereinafter based on preferred embodiments with reference to the drawings. The drawings are of a schematic nature and are intended to improve the understanding of the present invention. The same elements are denoted by the same reference signs.

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DETAILED DESCRIPTION OF THE INVENTION

[0032] Figures 1 - 4 show a preferred embodiment of the femoral stem offset adjustment system / instrument 1 (hereinafter referred to as adjustment system 1) according to the present invention. The adjustment system 1 is for adjusting (correctly positioning) a (trial) femoral implant 2 (especially a lower limb femoral implant) with respect to the intramedullary canal 3 of the femur. To achieve the desired posterior placement of the femoral implant 2, the adjustment system 1 guides the adjustment of the offset position of the femoral implant 2 with respect to a (trial) stem 4 corresponding to the intramedullary canal 3.

[0033] The adjustment system 1 includes a femoral support portion 5. The femoral support portion 5 is adapted to be connected to the femoral implant 2. The femoral support portion 5 statically attaches / fixes the femoral support portion 5 to the femoral implant 2. That is, the orientation of the femoral implant 2 corresponds to the orientation of the femoral support portion 5.

[0034] The adjustment system 1 includes a user adjustment element 6. The user adjustment element 6 is distally connected to the femur support part 5. The user adjustment element 6 is rotatably held by the femur support part 5 about a rotation axis. The rotation axis corresponds to the longitudinal axis of the adjustment system 1. That is, the user adjustment element 6 is attached to the femur support part 5 such that the femur support part 5 and the user adjustment element 6 are rotatably held relative to each other. The user adjustment element 6 is integrally and translationally connected to the femur support part 5. That is, the user adjustment element 6 is attached to the femur support part 5 such that the femur support part 5 and the user adjustment element 6 are translationally connected to each other (such that no relative displacement occurs between the femur support part 5 and the user adjustment element 6).

[0035] The adjustment system 1 includes a stem support part 7. The stem support part 7 is adapted to be connected to the intramedullary canal 3, in particular to the stem 4. The stem support part 7 statically attaches / fixes the stem support part 7 to the stem 4. That is, the orientation of the stem 4 corresponds to the orientation of the stem support part 7. The stem support part 7 is proximally connected to the user adjustment element 6. The stem support part 7 is integrally and rotatably connected to the user adjustment element 6. That is, the stem support part 7 is attached to the user adjustment element 6 such that the stem support part and the user adjustment element 6 are rotationally connected to each other (such that no relative rotation occurs between the user adjustment element 6 and the stem support part 7). The stem support part 7 is received / connected to the user adjustment element 6 so as to be slidable along a sliding axis. The sliding axis is perpendicular to the rotation axis. That is, the stem support part 7 is attached to the user adjustment element 6 such that the stem support part 7 is slidable along the sliding axis relative to the user adjustment element 6.

[0036] In other words, the adjustment system 1 functionally connects the femur support portion 5 (i.e., the femur implant 2) to the stem support portion 7 (i.e., the stem 4). By combining rotation about the axis of rotation and sliding of the user adjustment element 6 (perpendicular to the axis of rotation) along the sliding axis with respect to the stem support portion 7, the adjustment system 1 can adjust the offset translational movement of the femur support portion 5 with respect to the stem support portion 7 along any desired direction perpendicular to the axis of rotation (i.e., any offset direction on the plane perpendicular to the axis of rotation).

[0037] The adjustment system 1 includes a first link member 8 that attaches the femur support portion 5 and the user adjustment element 6 such that the femur support portion 5 and the user adjustment element 6 are rotatable relative to each other. The adjustment system 1 includes a second link member 9 that attaches the user adjustment element 6 and the stem support portion 7 such that the user adjustment element 6 and the stem support portion 7 are rotationally fixed relative to each other. The adjustment system 1 includes a third link member that slidably connects the user adjustment element 6 and the stem support portion 7.

[0038] At least two of the first link member 8, the second link member 9, and the third link member, preferably their longitudinal axes, are arranged on a substantially common plane, and that plane is perpendicular to the axis of rotation. Substantially on a common plane means not only the exact arrangement on the plane and the tolerance range of the plane, but also the arrangement within a common axial range that can extend from 0 mm (exact arrangement on the plane) to a maximum of 10 mm along the axis of rotation (a slight axial offset between at least two of the first link member, the second link member, and the third link member), preferably from 0 mm to a maximum of 5 mm (a small axial offset between at least two of the first link member, the second link member, and the third link member).

[0039] In the preferred embodiment shown in FIGS. 1 to 4, the longitudinal axis of the first link member 8 and the longitudinal axis of the second link member 9 are on a common plane perpendicular to the longitudinal direction of the adjustment system 1. In particular, the first link member 8 and the second link member 9 are integrally formed by a fastening element 10. The radially outer portion of the fastening element 10 forms the first link member 8. The radially inner portion of the fastening element 10 forms the second link member 9.

[0040] The radially outer portion forming the first link member 8 engages with the circumferential groove 11 of the femoral support portion 5. The circumferential groove 11 is formed on the inner circumferential surface of the femoral support portion 5. The circumferential groove 11 is a 360° circumference that provides 360° free rotation of the user adjustment element 6. The first link member 8 engages with the circumferential groove 11 so that the user adjustment element 6 and the femoral support portion 5 are translationally connected to each other.

[0041] The radially inner portion forming the second link member 9 engages (contacts) with the outer edge surface 12 of the stem support portion 7. The second link member 9 engages with the outer edge surface 12 so that the user adjustment element 6 and the stem support portion 7 are rotationally connected to each other. The outer edge surface 12 is perpendicular to the longitudinal axis of the second link member 9. Therefore, the user adjustment element 6 and the stem support portion 7 are freely translationally slidable along the outer edge surface 12. The outer edge surface 12 is proximal to the axial end surface 13 of the stem support portion 7. The second link member 9 projects radially inward so as to engage proximally / axially behind the axial end surface 13. Therefore, the user adjustment element 6 and the stem support portion 7 are connected to each other in the axial direction corresponding to the longitudinal axis.

[0042] The fastening element 10 is formed by two pins. These pins are coaxially arranged with each other. These pins are axially spaced apart. These pins are arranged at circumferentially opposite positions. Each pin passes through a hole in the user adjustment element 6. The pins are arranged on both sides of the stem support portion 7, and each contacts the outer edge surface 12 of the stem support portion 7. That is, the translational movement of the stem support portion 7 is guided by the two pins.

[0043] The third link member is formed by the first sliding portion 14 of the stem support portion 7 and the sliding guide portion 15 of the user adjustment element 6. The first sliding portion 14 has a rectangular shape that is long in the sliding axis direction. The first sliding portion 14 is received in the corresponding sliding guide portion 15 of the user adjustment element 6. The sliding guide portion 15 has a rectangular shape that is long in the sliding axis direction. The first sliding portion 14 and the sliding guide portion 15 attach the adjustment element 6 and the stem support portion 7 so that the adjustment element 6 and the stem support portion 7 can slide relative to each other along the sliding axis.

[0044] The third link member is formed by the second sliding portion 16 of the stem support portion 7 and the fastening element 10. The second sliding portion 16 has a rectangular shape that is long in the sliding axis direction. The second sliding portion 16 forms the outer edge surface 12. The outer edge surface 12 engages / comes into contact with the fastening element 10, particularly the radially inner portion of the fastening element 10. The second sliding portion 16 and the fastening element 10 attach the adjustment element 6 and the stem support portion 7 so that the adjustment element 6 and the stem support portion 7 can slide relative to each other along the sliding axis.

[0045] The adjustment instrument 1 includes an offset direction scale 17 that indicates the adjusted rotational position of the user adjustment element 6 with respect to the femur support portion 5. The offset direction scale 17 is formed by numbers on the outer peripheral surface of the user adjustment element 6 that indicate the clockwise position of the user adjustment element 6 with respect to the reference mark 18 on the outer peripheral surface of the femur support portion. The rotational position of the user adjustment element 6 with respect to the femur support portion 5 may be adjusted by 360°.

[0046] The adjustment instrument 1 includes an offset amount scale 19 that indicates the adjusted sliding position of the user adjustment element 6 with respect to the stem support portion 7. The offset amount scale 19 is formed by a window 20 provided on the user adjustment element 6, particularly the axial end face 13, and an offset mark 21 on the end face of the stem support portion 7. The sliding position of the user adjustment element 6 with respect to the stem support portion 7 may be adjusted from 0 to 5 mm.

[0047] The femur support portion 5 includes a femur attachment member 22 that fixedly connects the femur implant 2 to the femur support portion 5. The stem support portion 7 includes a stem attachment member 23 that fixedly connects the stem 4 to the stem support portion 7.

[0048] FIG. 3 shows the femur implant 2 attached to the adjustment instrument 1. The femur implant 2 includes an extension end face 26, with respect to which an extension gap between the tibia and the femur is set. The femur implant 2 includes a flexion end face 27, with respect to which a flexion gap between the tibia and the femur is set. It can be seen that the axial end face 13 does not protrude beyond the extension end face 26 in the axial direction (nor does it protrude beyond the flexion end face 27 in the radial direction). Therefore, the flexion gap and the extension gap can be evaluated while the adjustment instrument 1 is arranged.

[0049] Figures 4 to 10 show the use of the adjustment instrument 1. Figure 4 shows the adjustment instrument 1 before attaching the femoral implant 2 and the stem 4. In the first step (Figure 5), the adjustment instrument 1 (stem support portion 7) is connected to the (trial) stem 4 corresponding to the femoral intramedullary canal 3. The stem attachment member 23 is inserted into the stem 4. In the second step (Figure 6), the adjustment instrument 1 (femoral support portion 5) is connected to the (trial) femoral implant 2. The femoral attachment member 22 engages with the corresponding recess 24 of the femoral implant 2. In the third step (Figure 7), the adjustment instrument 1 (stem 4) is inserted into the femoral intramedullary canal 3. In the fourth step (Figure 8), by adjusting the offset direction (rotating the user adjustment element 6 with respect to the femoral support portion 5) and adjusting the offset amount (sliding the user adjustment element 6 with respect to the stem support portion 7), the femoral implant 2 is arranged to fit the femur. The femoral implant 2 is attached to the femur by the femoral fastening element 25. Since the adjustment instrument 1 does not protrude beyond the surface of the femoral implant 2, particularly the extension end face 26 (or the flexion end face 27), it is possible to perform a trial reduction of the flexion gap and a trial reduction of the extension gap while the adjustment instrument 1 remains attached to the femur (without removing the adjustment instrument 1). For the trial reduction of the flexion gap (Figure 9), the flexion distance template 28 is arranged in contact with the surface of the tibia and the flexion end face 27. For the trial reduction of the extension gap (Figure 10), the extension distance template 29 is arranged in contact with the surface of the tibia and the extension end face 26.

[0050] The offset amount and the offset direction are indicated on the offset direction scale 17 and the offset amount scale 19 of the adjustment instrument 1. Thus, the final implant can be arranged in the same position / orientation as the (trial) femoral implant 2.

Claims

1. A femoral stem offset adjustment system for adjusting a femoral implant with reference to the intramedullary canal of the femur, wherein the adjustment system comprises a femoral support adapted to be connected to the femoral implant, a user adjustment element rotatably held by the femoral support about a rotation axis, a stem support adapted to be connected to the intramedullary canal, the stem support being integrally rotatably connected to the user adjustment element and slidably connected to the user adjustment element along a sliding axis perpendicular to the rotation axis, and the femoral stem offset adjustment system includes, in the femoral support, a first link member rotatably holding the user adjustment element, a second link member integrally rotatably connecting the user adjustment element and the stem support, and a third link configuration slidably connecting the user adjustment element and the stem support, characterized in that at least the first link member and the second link member are arranged on a substantially common plane perpendicular to the rotation axis. Femoral stem offset adjustment system.

2. The femoral stem offset adjustment system according to claim 1, characterized in that the first link member and the second link member are integrally formed by fastening elements.

3. The femoral stem offset adjustment system according to claim 2, characterized in that the radially outer part of the fastening element forms the first link member, and the radially inner part of the fastening element forms the second link member.

4. The femoral stem offset adjustment system according to claim 2, characterized in that the fastening element is formed by two pins, the pins being coaxially arranged and axially spaced apart.

5. The femoral stem offset adjustment system according to claim 1, characterized in that the first link member engages a circumferential groove of the femoral support.

6. The femoral stem offset adjustment system according to claim 1, characterized in that the second link member engages an outer edge surface of the stem support, the outer edge surface being perpendicular to the longitudinal axis of the second link member.

7. The thighbone stem offset adjustment system according to claim 1, wherein the third link configuration is arranged substantially on the same plane as the first link member and the second link member.

8. The third link configuration includes a first sliding portion of the stem support portion and a sliding guide portion of the user adjustment element that receives the first sliding portion. The thighbone stem offset adjustment system according to claim 1, wherein the sliding guide portion and / or the first sliding portion has a rectangular shape that is long in the direction of the sliding axis.

9. The third link configuration includes a fastening element firmly connected to the user adjustment element and a second sliding portion of the stem support portion that receives the fastening element. The thighbone stem offset adjustment system according to claim 2, wherein the second sliding portion has a rectangular shape that is long in the direction of the sliding axis and forms the outer edge surface.

10. The thighbone stem offset adjustment system according to claim 1, further comprising an offset direction scale indicating the adjusted rotational position of the user adjustment element with respect to the thighbone support portion.

11. The thighbone stem offset adjustment system according to claim 1, further comprising an offset amount scale indicating the adjusted sliding position of the user adjustment element with respect to the stem support portion.

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